Acid Rain

Craig Spears

Feb 12, 2007

What is the pH of pure rainwater? Did you say 7? If so it’s a good guess, but not actually what is falling from the sky.

Carbon dioxide in the air is dissolved into the water and then forms carbonic acid (H2CO3). In normal conditions, rainwater is actually acidic – specifically it has a pH on average of 5.6.

So if all rain is acidic, what makes something acid rain? Quite simply, any rain with a pH under 5.6 is considered acid rain (though it is typically reserved for rain with a pH under 5). This is important to most people concerned with oil and natural gas because one major source of acid rain is sulfuric acid, H2SO4, formed in the atmosphere from SO2. (The other major source is HNO3, formed from NOx, so also keep up your cars’ maintenance).

Volcanoes and decomposing plants are the primary sources of the SO2 that forms the sulfuric acid in the atmosphere. However, the volcanoes spew their gases up into the high atmosphere which diffuses relatively quickly, and the decomposing plants are primarily in large quantity where people are not found.

What this means is that even though people are not the predominate source of SO2, we ARE the predominate source of SO2 that is near us. Limiting the amount of these acid rain precursors is the only way to effectively reduce the product and devastation (acid rain effects) it causes.